Reactor with axially disposed heated tube with valve

ABSTRACT

AN ADIABATIC REACTOR HAS AXIALLY POSITIONED THEREIN A VERTICAL JACKETED TUBE PROVIDED WITH AN AUGER TO CIRCULATE MATERIAL THROUGH THE TUBE, SAID TUBE HAVING A VALVE MEANS AT THE BOTTOM THEREOF TO RESTRICT CIRCULATION. TEMPERATURE WITHIN THE JACKETED TUBE IS SENSED AND SIGNAL GENERATED THEREBY UTILIZED TO CONTROL HEAT TO SAID JACKET AND TO OPEN SAID VALVE.

' March 2 1911 .5. 1c. CHRISTENSEN 3,567,402

REACTOR WITH AXIALLY DISPOSEDY HEATED TUBBYWITH VALVE Original FiledNov. 2, 1964 LMONOMER 49' PRODUCT v INVENTOR. I 0.6. CH RI ST E NS ENSOLVENT STEAM S CQNDENSATE CATALYST) A TTOPNEVS United States PatentOfice Patented Mar. 2, 1971 3,567,402 REACTOR WITH AXIALLY DISPOSEDHEATED TUBE WITH VALVE Don C. Christensen, Bartlesville, kla., assignorto Phillips Petroleum Company Original application Nov. 2, 1964, Ser.No. 408,184, now Patent No. 3,438,952, dated Apr. 15, 1969. Divided andthis application Jan. 17, 1969, Ser. No. 792,080

Int. Cl. C08f 1/98 US. Cl. 23-285 3 Claims ABSTRACT OF THE DISCLOSURE Anadiabatic reactor has axially positioned therein a vertical jacketedtube provided with an anger to circulate material through the tube, saidtube having a valve means at the bottom thereof to restrict circulation.Temperature within the jacketed tube is sensed and signal generatedthereby utilized to control heat to said jacket and to open said valve.

This is a division of my copending application Ser. No. 408,184, filedNov. 2, 1964, now US. 3,438,952.

The present invention relates to polymerization reactors. In one aspectthe invention relates to batch reactors designed to facilitate batchpolymerizations carried on in viscous reaction media in an adiabaticsystem. In another aspect the invention relates to a batch reactionvessel which provides excellent mixing and temperature control ofpolymerizing masses during the manufacture of polymers therein. In yetanother aspect, this invention re lates to a batch solutionpolymerization and copolymerization of olefin monomers in which heat isnot intentionally removed from the system by venting, cooling or thelike.

The success of a given polymerization process is generally measured bythe properties, or qualities, and more specifically the uniformity ofproperties exhibited by the resulting polymer product and by thequantity of polymerized product produced from a given amount of startingmonomeric material. Considerable difiiculty has been encountered in thecarrying out of solution polymerization of olefin monomers on acommercial scale because of the problems in controlling the temperaturewithin the batch reactor. The polymerization reaction is exothermic andit is, therefore, necessary to effect continuous withdrawal of heat fromthe reacting zone. However, this is complicated by the fact that in manycases the polymers produced remain in solution in the solvent. Theseviscous solutions of polymers constitute very poor heat transfer media.It is possible to improve the heat transfer by effecting continuousagitation so as to keep the body of the reaction mixture continuously inmotion. However, experience has shown that even the best types ofagitators will fail to produce the desired results. Since the viscosityof the reaction mixture is a function of the concentration of thepolymer therein, one method of overcoming the heat transfer problemsreferred to above is to operate with a low concentration of polymer inthe reaction mixture. This is an undesirable expedient since, if thepoly "mer concentration is reduced, the output of polymer for a givensize reaction system is reduced by a corresponding amount. Such reducedoutput has had to be tolerated in the past because no method forcarrying out batch solution polymerization processes of olefin monomershas been capable of effecting the necessary withdrawal or utilization ofreaction heat when operating with very viscous solutions of high polymercontent. This is particularly true in the case of some polymers wherethe properties of the polymer obtained are considerably impaired if thetemperature in the reaction zone is allowed to rise to too high a value.

In devising a batch process for exothermic polymerizations, andconjunctively the apparauts to be used in the same, two aspectsprominently affect success. The first is the ability to extract and/orutilize heat generated by the reaction and the second is the capacity toprovide contact between the reactants. Both must be provided for;otherwise, the resulting polymerized products possess nonuniformproperties and low monomer conversion values may be experienced.

In accordance with the present invention, I have discovered thatexcellent synthetic rubber polymers can be obtained in the solutionpolymerization of the olefin monomer in the presence of a suitablecatalyst, if polymerization is first initiated on a small fraction ofthe total volume of the reactant solution and this small fraction ispermitted to circulate through the bulk of the reaction mixture wherethe heat of reaction of the initiated volume is used to initiate theremaining bulk. This adiabatic heating of the bulk of the reactants bythe small volume which is preinitiated permits the initial reactiontemperature of the polymerizing mixture to be lower than obtainable byprior art procedures and consequently to exhibit a lower final peaktemperature. Ordinarily the polymerization must be initiated at atemperature between -180 F.; however, with my procedure, the reactioncan be initiated as low as 50 F.

Accordingly, it is an object of the present invention to providereactant apparatus in which to carry on batch adiabatic polymerizationreactions in solutions which achieve high concentrations of polymer.

A further object is to provide batch polymerization reactors whichprovide excellent mixing and temperature control of polymerizing massesduring the manufacture of polymers.

A still further object is to provide batch polymerization reactors whichpermit lower average initiation temperatures for the polymerizingmasses.

Another object is to provide polymerization reactors in which theconcentrations of both the solvent and the catalyst can be appreciablyreduced without causing degradation of properties exhibited by theresulting polymer product.

Yet another object of the present invention is to provide a process foreffecting solution polymerization of olefin monomers which is capable ofoperating terminally with high concentrations of polymers wherein theheat of reaction released in this exothermic polymerization and absorbedby the system still maintains the final temperature below apredetermined peak temperature.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description which is to beconsidered in connec tion with the accompanying drawing, in which:

In the drawing there is shown a partial cross sectional view ofapparatus for carrying out the method of the invention.

Referring to the drawing, wherein a reactor 1, of the type presentlypreferred is illustrated:

Reactor 1 comprises a short vertically-designed cylindrical casing 3 ofrigid construction. Within the reactor 1 there is suitably mounted ahollow draft tube 5 having a circular cross section, and beingsurrounded by a heating jacket 7 forming an annulus 10 through whichsteam from line 9, being regulated by control valve 11 (as hereinafterdescribed), is circulated and its condensate exhausted through line 13.This jacketed tube 5 forms a confined mixing zone located within thereactor. The diameter and length of tube 5 is constructed to enclose avolume which is from 2 to 10 percent, preferably about 5 percent, of thetotal volume of reactor 1. A suitable insulating means 15, which isimpervious to the reactant mixture, surrounds the jacket 7. V

One end 6 of the tube is open while its other end is closed by atemperature-actuated discharge valve 17. The position (relative opening)of this valve is caused to be regulated by temperature controller 43(hereinafter described) in order to discharge reactant mixture containedin tube 5, whichhas been autothermically heated by the polymerizationreaction, at a rate corresponding to the rate of polymerization heatevolution so that, at least in the early part of the reaetion period,the temperature in the tube reaches and maintains but does notsubstantially exceed temperature controller 43 set point (predeterminedvalue). This valve means 17 thereby cooperates in a novel manner withthe draft tube 5 in relation to the rate of initiation of the reactantscontained in the draft tube and the consequent generation of heatmanifested by adiabatic rise of the temperature of the reactant mixture.

Monomer feed is introduced through line 38, solvent is introducedthrough line 39, and the catalyst is introduced into the bottom of thedraft tube 5 through line 41. At the conclusion of the batchpolymerization reaction product is withdrawn from the reactor throughline 49.

At the start of any batch polymerization, valve 11 is 'in its wide openposition and valve 17 is in its closed position. The temperaturemeasurement signal emitted by a sensing element 45, positioned in tube 5and operatively connected to a temperature controller 43, is below a setpoint (S;P.) which is preset at a desired temperature value according tothe characteristics desired in the product of the particularpolymerization reaction. The controller 43 is a conventional product ofa number of instrument manufacturers; such as The Foxboro Company ofFoxboro, Mass., whose Model 58 controller such as described in Bulletin17-169, August 1953, of The Foxboro Company is an example thereof.

As the temperature inside the tube 5 increases, the controller 43 inresponse to a temperature measurement signal from sensing element 45provides an output signal which is related to the deviation of themeasured temperature from the set point. This output signal graduallyincreases and closes valve 11 as the measured temperature approaches theset point value due to the heat input from the condensing steam and/orfrom the exothermic reaction heat. At the mid signal produced by thecontroller 43 both the valves 17 and 11 are closed. At the maximumsignal produced by controller 43, valve 17 is wide open and valve 11remains closed. As the temperature rises above the set point due toincreasing liberation of reaction heat, the signal produced bycontroller 43 causes the diaphragm in valve operator 47 to movegradually downward causing the valve 17 to be gradually opened therebypermitting the contents of tube 5 to pass into the annular space 8 whichcontains the bulk of the reactant mixture. The active polymerizingmolecules seed or initiate reaction in the bulk thus causing wide spreadreaction within the reactor. As the reaction temperature 45 rises, valve17 opens wide allowing free circulation of reactor contents throughoutthe vessel.

The reaction mixture in the draft tube 5 is caused to move downwardlywithin the draft tube by means of an auger 19 carried by a shaft 21mounted for rotation in bearing 23. A collar 25 is fixed to the shaft 21for rotation therewith and carries two arms 27 extending at right anglesto the shaft 21. At their ends remote from the shaft 21 each of the arms27 has secured thereto an arm 29 extending downwardly into an annularspace 8 defined by the outer wall of insulated jacket 7 of draft tube 5,and the inner side wall of the casing 3. A vertical mixing ribbon 31 issecured to each of the arms 29 by welding or the like. It will beunderstood that any suitable means for securing the ribbon to the arms29 can be employed. This particular assembly permits the reactionmixture to be circulated downwardly through the interior of the drafttube 5 and upwardly through the annular reaction volume 8. Since theonly heat supplied to this system is to the draft tube 5 which isinsulated from the volume 8; this circulation of the reaction mixture,once initiated, serves not only to keep. the contents of :the reactor 1well mixed but also to promote heat transfer between the small fractionof the highly-reacting reaction mixture in the draft tube and thelesser-reacting bulk of the reaction mixture in the annular volume 8.

With the aid of apparatus of the type described, it has been foundpossible to conduct batch polymerizations of olefin monomers at muchhigher viscosities, at lower (averaged) initiation temperatures, andwith a reaction g mixture having a lower solvent-to-monomer ratio thanwas possible using the conventional apparatus heretofore known.

This apparatus is generally applicable to the solution polymerizationand copolymerization of olefin monomers. General reference herein topolymers is intended to cover; both homopolymers and copolymers. Thenature of the monomer, the catalyst or the solvent is not a criticalfeature of the'invention. Solution polymerization of olefin monomers,especially ethylene, is now well known. Various olefins such asethylene, propylene, butylene, butadiene, isoprene, styrene, and thelikecan bepolymerized at relatively low pressures and temperatures toproduce high molecular weight polymers and copolymers using a processinvolving an organolithium initiator. This process is usually carriedout in the presence of an organic solvent such as butane, pentane,hexane, cyclohexane, butenes, pentenes, benzene, toluene, chlorobenzene,and the like, at temperatures between about 50 F. and 240 F.

In order to illustrate the operation of my invention to show the new andunexpected advantages which are derived therefrom andto demonstrate thedimensional relationship between the various components of reactor 1,one embodiment of such a reactor had the following dimensions:

DRAFT TUBE 5 Inside diameter-21 inches. Lengthinches. Volume inside ofdraft tube-450 gallons.

AUGER 19 Diameter20 inches. Height99 inches. Pitch8 /z inches.

CASING 3 Inside diameter-72 inches.

Height (head-to-head)l92 inches. Scraped height-172 inches.

Contains a mixing ribbon on a 40-inch pitch.

Total liquid volume (iess draft tube, valve, auger, ribbon, etc.) is3000 gallons. Approximately 5 percent of this volume or U.S. gallons isheld within the draft tube.

With the aid of apparatus of the type shown in the drawing, it has beenfound possible to conduct polymerization of olefin monomers at muchhigher viscosities (and therefore higher polymer concentrations) andwith much lower average initiation temperatures than was feasible whenoperating with a reactor provided only with cooled surfaces and meansfor agitating the contents of the re- 7 actor with a means such as theauger 119 or a propeller or The valve 17 at the start of the operationis in the closed position. The valve 17 is opened and the reactionmixture consisting of the monomer, catalyst, and solvent is stirred byrotating the shaft 21 at a speed of 30 r.p.rn., which gives a turnovertime of the entire reactant contents on the order of 1-3 minutes. Thevalve 17 is then closed whereby approximately 150 gallons of thereaction mixture are isolated from the remainder of the feed mixture.Mixing is continued and steam is supplied to the heating jacket 7 inorder to raise the temperature of the reactant mixture contained in tubeto 160 F. whereupon polymerization therein is initiated. The sensingelement 45 transmits a temperature measurement signal to controller 43.As the temperature inside tube 5 approaches 160 F. then this controllerproduces a signal which causes steam flow valve 11 to gradually closeand which then causes diaphragm 47 to gradually open valve 17. Theopening of valve 17 permits that part of the reaction mixture in tube 5to pass into the annular space 8 which holds the bulk of the reactantmixture. The closing of valve 11 stops the flow of steam into theannular heating space 10 via line 9. This control system is adjusted sothat at a temperature of 160 F. inside the tube 5, the valve 11 will becompletely closed and the valve 17 will be starting to open. Obviouslyone skilled in the art could, by calibration of the valves and of thecontroller, provide overlapping of the closing of valve 11 with theinitial opening of valve 1747. Similarly, a dead zone could be imposedwhereby valve \11 would be fully closed, e.g., 155 F. with valve 1747beginning to Open at 180 F.

The rate of heating of the relatively cold reaction mixture contained intube 5 to a temperature where initiation of the polymerization reactiontakes place is dependent upon physical parameters such as the volume ofthe initiator section, the heating surface provided by tube 5, the steampressure (and temperature) within space 10 and the degree of agitationprovided by auger 19. Such a rate of temperature rise can be in therange of 1 to 10 F. per minute, preferably about 5 F. per minute.

Similarly, the rate of temperature rise of the reactor contents uponinitiation of polymerization by the small reacting volume is dependentupon the volume ratio and upon the activity of the catalyst,concentrations of reaction poisons, etc. In most cases, the temperatureincreases slowly (at a rate of 0.1 to 2.0 degrees per minute) for a fewminutes, then accelerates rapidly to a rate in the range of 1 to 10degrees per minute thereafter decreasing gradually to a rate of 0.1 to2.0 degrees per minute as the reactant(s) is depleted and heat lossesfrom the reactor to its surroundings becomes large due to the elevatedtemperature, e.g., about 200 F. Because of this non-linear adiabatictemperature rise behavior, monomer conversions of 98 percent and aboveare infrequently accomplished since the reaction time required becomesexcessive. Generally, economical practice in polymer manufacturingplants dictates carrying reactions of this character to 98 percent orless of completion, often in the range of 80 to 98 percent.

The controller 43, in response to a temperature measurement signal fromsensing element 45 provided an output signal related to the deviation ofthe measured temperature from the set point (S.P.) In this experimentthe desired temperature was set at 160 F.

The mixture initiated as hereinabove described produces a seeding effectin the bulk of the reactant mixture and initiates the polymerization ofthe remainder of the feed mixture at or slightly above the chargetemperature of the charge mixture. Because of this low initiationtemperature and because of the relatively low solvent-tomonomer ratio,the temperature of the reaction mixture does not rise above 240 F. Itis, therefore, unnecessary to provide a venting or any type of coolingof the reactants and it is possible to employ a high monomerconcentration without exceeding a desired peak temperature.

This permits polymer to be produced at arate of 1500 pounds per hourwith about percent conversion of the butadiene-styrene feed.

The polymer solution is removed from the reactor through line '49 afterapproximately 1 /2 to 2 hours residence time. The polymer containedtherein possesses a Mooney viscosity of about 49-50. The solidsconcentration in the reaction mixture withdrawn from the reactor is 17.7percent.

, In another embodiment, the valve 117 at the start of the operation isin the open position. Monomer and solvent are added to the reactor andstirred by rotating the shaft 21. Valve 17 is then closed to isolateapproximately gallons of the monomer and solvent mixture. Catalyst isthen introduced into the bottom of tube 5 and auger 19 is rotated onshaft 21 to circulate the catalyst within the tube 5. As describedhereinabove, steam is supplied to the jacket 7 in order to raise thetemperature of the mixture contained in tube 5 to F. By confining thecatalyst to the area inside of the tube, substantially all of thecatalyst will be initiated when the valve 17 begins to open.

This superiority of the method of the invention over methods utilizing aconventional reactor can be compared by using the same polymerizationsystem. In a conventional reactor. solvent-to-monomer weight ratio in astyrene-butadiene in n-hexane system was in the neighborhood of1050-100. The weight ratio of solvent to monomer to catalyst was 1050/100/0.85. The ratio of the catalyst was the same. Polymer was producedin this reactor at the rate of 800 pounds per hour with about 90 percentconversion of the feed with a residence time in the reactor of 1 /2-2hours. The solids concentration in the reaction mixture in thispolymerization process withdrawn from the reactor was 8.6 percent. Themaximum reaction temperature was 240 F. in this system also. Theinitiation temperature (of the entire reactor contents) was 160 F. Itcan be readily observed that the conventional methods require a highersolvent-to-monomer ratio, produce less polymers per hour.

It is also Within the scope of my novel process in those cases Whereparticularly great difiiculty is encountered in maintaining the reactionmixture below a desired peak temperature to either precool the reactionmixture before it is introduced into the reactor or precool theindividual reactants before they are mixed therein. However, I havediscovered that precooling the bulk of the reactants below 50 F. woulddecrease the activity of the butyl-lithium catalyst to such an extentthat the seeding effect of the preinitiated small fraction of the totalvolume of reactants charged would fail to cause an initiation of theentire mass. 7

The invention has been described with particular reference to theproduction of a copolymer of styrene and 1,3-butadiene but is equallyapplicable to the production of any other polymer by a batch solutionpolymerization process resulting in a viscous solution of the polymer.The upper limit of viscosity at which the method of the invention can beeconomically practiced is dictated not by the extent to which heattransfer from the reaction mixture is feasible, but rather by practicallimitations such as the power required for effecting movement of theauger and ribbon elements.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described herein.

I claim:

1. An adiabatic batch polymerization reactor comprising a hollow casinghaving a reaction zone therein; closure means located within saidreaction zone for enclosing a portion of the reaction zone, said closuremeans being open at the top thereof; temperature measuring means locatedin the closure means and being operatively responsive to changes oftemperature therein; heating means positioned around the closure meansfor raising the temperature of that portion of the reaction zone locatedWithin the closure means; valve means located in the bottom of theclosure means; controlling means being operatively responsive to saidtemperature means for gradually opening said valve means and forgradually shutting off said heating means in response to the temperatureinside the closure means.

2. A reactor according to claim 1 further including agitation means forcirculating a reaction mixture through the reaction zone and downthrough the closure means.

3. An adiabatic batch polymerization reactor comprising a closed,vertically-disposed hollow cylindrical casing having a reaction zonetherein; a hollow draft tube located within said reaction zone andenclosing about 2 to 10 percent of the volume of the reaction zone, saiddraft tube being open at the top thereof; a valve means located in thebottom of the draft tube; a heating jacket surrounding said draft tubefor receiving heat transfer fluid; insulation means located on theoutside of said heating jacket; a temperature-sensing means positionedwithin said draft References Cited UNITED STATES PATENTS 2,472,3776/1949 Keith 23288.35X 2,488,406 11/ 1949 Hirsch 23-288.35X 2,557,8426/1951 Ruthrufl 23288.35X 3,074,924 1/1963 Kizer et al. 26095 3,206,2879/1965 Crawford 23285 JAMES T. TAYMAN, JR., Primary Examiner US. Cl.X.R.

